In a wireless charging system, a wireless power transmitting device such as a device with a charging surface wirelessly transmits power to another electronic device such as a battery-powered, portable electronic device. The portable electronic device receives the wirelessly transmitted power and uses this power to charge an internal battery and to power components in the portable electronic device. Foreign objects in proximity to a wireless power receiving device can intercept power intended for the wireless power receiving device. It is desirable to reduce power transfer to foreign objects during wireless charging operations.